Gaskets are often used as a seal between mating mechanical components. One common application involves gasket placement between the engine block and the cylinder head of an internal combustion engine. Cylinder head gaskets typically extend around the cylinder bores to provide a combustion seal, maintaining the high temperature gases of combustion within the cylinder bores. At the same time, the gaskets also seal fluid flow openings such as coolant and oil openings to prevent undesirable mixing. In addition, such gaskets prevent leakage by sealing the areas around the bolts which connect the cylinder head and engine block. The gasket bears the load from a bolted connection of the mechanical components and relies upon that load to provide a seal.
Gaskets can be made of a wide variety of materials and layers. Typically, cylinder head gaskets are constructed of at least two metal layers. An additional layer, or layers, which is known as a shim, may be located between the two metal layers, which are often referred to as the active gasket layers.
A shim is typically made of metal and may have a constant thickness. Shims typically are not compressible and thus may assist in creating a sealing feature for the gasket when the gasket is compressed.
Shims, however, do have some significant disadvantages. More particularly, when the gasket is compressed, the loading of the shim between the cylinder bores is typically poor. If the shim is not properly loaded, it may result in premature failure or overall poor performance of the gasket.
Furthermore, shims require extra metal material, thus increasing not only materials costs for the gasket, but also they also increase manufacturing costs. Shims also disadvantageously require mechanical locking features to secure them to another layer of the gasket. These locking features increase the cost of the gaskets and are subject to failure. Lastly, it is difficult to accurately adjust the thickness of a shim in a cost effective manner where variable shim thickness is preferred to tailor gasket loading.
What is sought is added sealing between the two outer metallic layers, without providing a shim layer, as a result reduced material and labor costs would be realized.